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Underground Tales: Karst

Arkansas Natural Heritage Commission - Friday, March 29, 2019

by Bryan Rupar, ANHC

A karst system is a type of landscape in which the bedrock (typically limestone, a sedimentary rock made of calcium carbonate) has been chemically weathered by groundwater over time. Karst systems can include springs, sinkholes, and caves.

Springs are formed when groundwater flows through a surface crack in the bedrock. Some springs are very large, discharging millions of gallons of water a day. Mammoth Springs, located in Fulton County, is one of those large springs, discharging 234 million gallons of water each day! Most springs are much smaller, with a limited flow of water.

A sinkhole is a naturally occurring shallow depression or a vertical opening to a cave created when surface limestone erodes. Sometimes called sinks, they occur in hilltops, hillsides, and valley bottoms. Sinkholes represent direct unfiltered paths from the surface to the groundwater systems below. Altering a sinkhole can alter the groundwater drainage patterns to springs and caves (Caring for Your Karst, Springfield Plateau Grotto).

Caves are an air-filled underground space large enough for human exploration. They are formed when limestone is dissolved by groundwater, widening cracks to form underground passages, and eventually caves. Caves provide habitat for many unusual species, including bats, a variety of invertebrates, salamanders, and blind cavefish. All of these organisms are characterized by adaptations that suit them for life in a dark, cool subterranean habitat.

The recharge zone for a spring or cave is defined as the area of land where surface water flows into the groundwater that eventually re-emerges in the cave or the spring. Karst regions contain underground aquifers, geologic formations that hold large portions of water. Approximately 25 percent of our nation’s groundwater is located in cave and karst regions, making this unique landscape a valuable supplier of freshwater.

Animals strongly associated with karst habitat are typically separated into three categories. Troglophiles (terrestrial fauna) and stygophiles (aquatic fauna) are those animals that can spend their entire life underground, but can also be found aboveground. The Cave Salamander (Eurycea lucifuga) is a good example of a troglophile (see Arkansas’s karst: salamanders call it home). The second category, called trogloxenes (terrestrial fauna) and stygoxenes (aquatic fauna), spend part of their life cycles in caves and part of it aboveground. Gray bats (Myotis grisescens) are examples of this class of animals. The third category, called troblobites (terrestrial fauna) and stygobites (aquatic fauna), are restricted just to life underground. The Ozark cavefish (Troglichys rosae), adapted specifically to living underground, is an example of this class.

An estimated 20 percent of the landscape of Arkansas is considered karst habitat, with the majority of that being located in the Ozark Plateaus.In addition to the groundwater resources they provide, karst habitat is critical for many plant (see Karst geology supports rare plants) and animal species. Due to their unique environmental characteristics, karst features contain a high number of rare and sensitive species.


Top left -- Foushee Cave Natural Area, Independence County, Arkansas. Photo by Bryan Rupar, ANHC.

Middle left --The Cave Salamander (Eurycea lucifuga) can spend its life either completely underground or outside of a cave. Photo by ANHC staff.

Bottom right -- Cave Spring Cave Natural Area, Benton County, Arkansas. Photo by Bryan Rupar, ANHC staff.





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